The idea of a monorail through beech forest in Fiordland had a Disneyish sort of appeal. Hardened trampers might be able to reach the treasures of the remote Snowdon Forest on foot, but many other people can't.

Deep-green conservationists might hate the idea of a comfortable ride in a pod through the rainforest. Others would have enjoyed the experience.

Conservation Minister Nick Smith was right, however, to reject the proposal. There was a huge amount of uncertainty about the effects on the environment, and the proposal never cleared it up. The monorail was to be placed inside a 200-metre wide "envelope", but the precise route wasn't specified. The developers promised they would use best practice in deciding where to build it, but that won't do. In a sense, Riverstone was asking the Government to buy a pig in a poke.

And there were deep doubts about whether the monorail was financially viable. The risk, as Smith said in his letter to Bob Robertson, the Monorail Man, was that a huge "white elephant" would be left in the forest without enough funds to remove it. These doubts were neither idle nor frivolous. They were fundamental.

Consultant Ian Dickson's review of the business case was devastating. He showed that Riverstone's estimates of the return were much too high, based as they were on outdated tourism figures and on over-optimistic estimates of their future growth. Of course, the developer disagrees with the figures. But Smith's duty is to be cautious.

If the project failed, after all, the long- term effect on the landscape would be enormous. Dickson's report suggested that the cost of removing the monorail might be as high as $270 million, a truly staggering amount, and much more than Riverstone's estimated cost of $210m to build it.

No New Zealand government would want to be left with 43 kilometres of railway track and concrete in a priceless piece of its natural heritage. The publicity would be globally embarrassing - a monument to the betrayal of our clean-green reputation. Robertson offered to pay a bond. Dickson suggested no bank would back the surety - and Smith agreed.

What else could he do? The risks of this project, both environmental and financial, were huge. Unless there was overwhelming evidence that the risks were justified, the answer had to be "No". It was possible, of course, that another company could take over the defunct monorail for nothing and make a go of it ("the early bird may get the worm, but the second mouse gets the cheese"). But as Smith pointed out, he couldn't back a project in the vague hope that a second mouse might arrive.

Nobody could accuse Smith of being prejudiced against the developers. It was National, after all, which wanted to rewrite the Resource Management Act in a way which, according to the critics, skewed the planning laws in favour of business. It was only a revolt by the Government's usually reliable helpers, the Maori Party and Peter Dunne, which forced National to cancel its planned revamp. But even a business-friendly government could see the problems with the Fiordland monorail.